This invention is related to electrical connectors and, more particularly, to electrical connectors in which the connector body is conformally coated and the contact tails are sealed to prevent the conformal coating material and other contaminants, such as solder and solder flux, from entering the connector body.
The trend toward greater complexity and miniaturization of printed circuit boards and connectors means that conformal coating is both more important and increasingly more difficult. The closer the line spacing, the more vulnerable the solder connections are to moisture and contaminants, heightening the need for protective coating. At the same time, the close contacts of connectors best suited to these boards are extremely difficult, time consuming and costly to mask properly before boards can be coated. The necessity for conformal coating is well established. Uncoated solder connections are vulnerable to moisture and contaminants which can lead to short circuiting or other malfunction.
Complex boards with closer line spacing present a higher potential for corrosion damage. Tin lead oxide can form on boards subjected to humidity, creating conductive paths between leads. Humidity and DC current also encourage dendritic growth or copper filaments plating out from one lead and growing toward another. The risk of either of these unwanted conducting paths in the connector solder terminations increases the need for protective coating.
Military standard, MIL-STD-275, Printed Wiring for Electronic Equipment, states:
Printed-wiring assemblies shall be conformally coated . . . . The coating shall be applied to both sides of the cleaned printed-wiring assembly, including the part leads.
To meet requirements for conformal coating, one alternative is to mask the entire connector to prevent coating material from penetrating the contact area during the coating process. An additional coating process is required to comply fully with military standards. Not only is extensive masking costly and slow, it is not 100% reliable. On occasion, some coating material wicks into the connector, interfering with proper insertion of the mating part. This can result in either a permanent loss of electrical connection, or an intermittent loss, which is even more difficult to locate and correct. In either case, the connector must be removed and replaced which is time consuming and labor intensive. Furthermore, there is a risk that damage can occur, potentially leading to scrapping the board at a cost of several thousand dollars.
In the box and post style connectors, and other types of connectors suitable for high density printed circuit board applications, contact tails extend from one side of a connector body, and the opposite side of the connector body is open to receive a mating connector pin. In many applications a conformal coating is desirably employed to coat the entire body of the connector, except for the openings where the mating pins enter the connector body. The conformal coating seals off the connector against moisture and foreign materials.
It is known that the conformal coating material must not enter the connector pin portion, since if it does it may prevent electrical contact between contacts in the body and mating contacts inserted into the connector. U.S. Pat. No. 4,645,278, issued Feb. 24, 1987, entitled "Circuit Panel Connector, Panel System Using the connector, and Method for Making the Panel System," which issued to Harold M. Yevak, Jr. et al, shows the use of a high-temperature-resistant tape of a polyimide material that has a layer of a high-temperature adhesive thereon. The tape is removably secured over the opening to seal off the openings where the mating connector pins are inserted.
In the Yevak, Jr. et al patent, an acrylic material is used for the conformal coating, and a flexible heat-curable, adhesive sealing material, such as a conventional epoxy, or silicone sealer is secured to the bottom of the connector body in the contact tails area. The connector of the Yevak, Jr. et al patent is mounted on a circuit panel and the heat-curable adhesive layer engages the circuit panel. The panel is than subjected to a heat treatment, such as occurs during soldering of the contacts to the circuit panel, and the adhesive layer is cured to adhere the bottom of the connector body to the circuit panel.
The use of epoxy or silicone sealing materials which are heat-curable during the soldering phase often will not seal off the base sufficiently to exclude solder or solder flux from the body of the connector. Moreover, silicone materials tend to prevent many commonly employed conformal coating materials from adhering properly to a coated connector, or associated printed circuit board.
U.S. Pat. No. 3,744,128, issued July 10, 1973, entitled "Process for Making R.F. Shielded Cable Connector Assemblies and the Products Formed Thereby," issued to Aaron Fisher et al, shows the use of a material which contains a thixotropic agent which is dispensed through a pressure gun cartridge into a R.F. shielded cable assembly. Because of the non-sagging nature of this bulk potting material it remains where it is applied. The potting material is heat-curable and very little subsequent flow occurs in the cable assembly.
In the Fisher et al cable assembly, once the cable and connector structure is potted with the flexible potting material, the entire exterior surface of the potting material, and portions of the adjacent connector housing are coated with an electrically conductive material. A supportive protective jacket is then placed over the conductive coating and the coated portion of the connector housing. The Fisher et al cable assembly, however, does not receive mating pins inside the body of the assembly, nor is its exterior conformally coated, as are the connectors of the Yevak, Jr. patent and of the present invention.